Interstellar Extinction in the Direction of the Aquila Rift

A&A 405, 585–590 (2003) Astronomy DOI: 10.1051/0004-6361:20030599 & c ESO 2003 Astrophysics

Interstellar extinction in the direction of the Aquila Rift

V. Straiˇzys1,K.Cernisˇ 1, and S. Bartaˇsi¯ut˙e1,2

1 Institute of Theoretical Physics and Astronomy, Vilnius University, Goˇstauto 12, Vilnius 2600, Lithuania e-mail: [email protected] 2 Astronomical Observatory of Vilnius University, Ciurlionioˇ 29, Vilnius 2009, Lithuania e-mail: [email protected]

Received 28 February 2003 / Accepted 14 April 2003

Abstract. The distance dependence of interstellar extinction in the direction of the Aquila Rift is investigated using 473 stars observed in the Vilnius photometric system. The front edge of the dark clouds in the area is found to be at 225 55 pc and ± the thickness of the cloud system is about 80 pc. The maximum extinction AV in the clouds is close to 3.0 mag. Two stars with larger extinction are found and discussed. Since the new distance of the clouds is larger than the previously accepted distance, the cloud system mass should be increased to 2.7 105 M which is close to the virial mass estimated from the CO velocity × dispersion. Additional arguments are given in favor of the genetic relation between the Serpens and the Scorpio-Ophiuchus dark clouds.

Key words. stars: fundamental parameters – ISM: dust, extinction – ISM: clouds – ISM: individual objects: Aquila Rift – ISM: individual objects: Serpens molecular cloud

1. Introduction Stars and other sources in the area have been well covered by the infrared surveys: by IRAS in the far infrared and Starting from Cygnus, in the direction of the Galactic center the by 2MASS in the JHK range. Also, numerous radioastronom- Milky Way appears to split into two branches. The southern ical studies in the lines of H I, CO, H2CO, NH3 and H2Oare branch runs through Cygnus, Vulpecula, Sagitta, Aquila and available in the area. The distribution of molecules, especially Scutum, entering the Galactic central bulge in Sagittarius. The of CO, shows a very close resemblance to the dust distribu- northern branch crosses Vulpecula and Aquila and disappears tion (see Dame & Thaddeus 1985; Dame et al. 1987, 2001). in the northern part of the Serpens Cauda and Ophiuchus con- According to CO radio observations, the Aquila Rift occupies stellations, being covered by numerous dust clouds. This com- a region of irregular form between 20◦ and 40◦ in Galactic lon- plex of dark clouds usually is called the Aquila Rift. gitude and between –6◦ and +14◦ in Galactic latitude. However, The distances and extinction properties of these clouds are some protrusions and blobs of gas and dust extend up to ` = 15◦ known only with low accuracy. So far the area is poorly inves- and b =+20◦. tigated by modern photometric methods in the optical range. About a decade ago we started a program of investiga- The collected UBV and MK data have been used for a crude es- tion of the Serpens Cauda clouds belonging to the Aquila timate of the dependence of interstellar extinction on distance Rift by photoelectric photometry of stars in the Vilnius seven- in the Rift direction (FitzGerald 1968; Neckel & Klare 1980; color photometric system (Table 1). Our first results were Forbes 1985 and others). A sudden appearance of reddened published by Straiˇzys et al. (1996), hereafter Paper I. The in- stars at 200–250 pc is observed. According to the summary of vestigation was based on photometry and photometric classifi- Dame & Thaddeus (1985), the estimated distance of the Aquila cation of 105 stars down to magnitude 13, located around the Rift is 200 100 pc. ± core of the Serpens molecular cloud mentioned above. The size A field around the core of one of the densest Serpens molec- of the area investigated was about 6.5 square degrees. It was h m ular clouds (at 18 30 , +1◦14.50, 2000.0) with active star for- found that the dust cloud in the area appears at a distance of mation has attracted more attention (see the review article by about 260 pc. Eiroa 1991). The distance of the cloud has been discussed by However, the area investigated in Paper I is only a small Strom et al. (1974), Chavarria et al. (1987, 1988), Zhang et al. part of the whole complex of the Aquila Rift. The newest cat- (1988), de Lara & Chavarria (1989), de Lara et al. (1991) and alog of dark clouds of Dutra & Bica (2002) enumerates in the Straiˇzys et al. (1996). Rift more than 50 clouds of different sizes. It is important to know whether all these clouds are at the same distance or they Send offprint requests to:V.Straiˇzys, e-mail: [email protected] form a system with a significant depth.

Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20030599 586 V. Straiˇzys et al.: Interstellar extinction in the Aquila Rift

Fig. 1. The chart for the investigated Serpens Cauda area with the following sub-areas: A is the sub-area investigated in Paper I; Ser I, Ser II, Ser III and Ser IV are the sub-areas in which photoelectric standards have been measured for future CCD photometry (Cernisˇ et al. 1997 and Paper III); SA 110 is the area in which HD stars have been measured by Zdanaviˇcius et al. (1978). The broken line at RA = 18h19m divides the area into two parts with diﬀerent dependence of AV on distance.

Table 1. Mean wavelengths and half-widths of passbands of the in Table 2. The measured stars in the sub-areas I–IV will be Vilnius photometric system. used as standards for future CCD photometry of fainter stars. Kapteyn Selected Area 110 is located at the edge of the same Passband UP X Y Z VS area. In it Vilnius photometry of 30 HD stars has been published by Zdanaviˇcius et al. (1978). These stars were also included λ (nm) 345 374 405 466 516 544 656 in the present study of interstellar extinction (see Table 2). ∆λ (nm) 40 26 22 26 21 26 20 Magnitudes and color indices of stars in the sub-areas are published in the papers listed in Table 2. Table 2. Four sub-areas in which fainter stars have been measured in In the present study the extinction data of 80 stars from the Vilnius photometric system and SA 110. Paper I were also used. Their distances are transformed to the new distance scale corresponding to the distance modulus of Sub- RA Dec Magnitude Number Publ. Hyades V MV = 3.3. Other stars of Paper I were rejected: area h m limits of stars − ◦0 some of them were found to be visual binaries and for some Ser I 18 01.3 –00 18 11.3–14.4 11 1 the classification accuracy from the photometric data was too Ser II 18 31.5 –00 50 11.0–13.4 4 2 low. They are either unresolved binaries or peculiar objects. Ser III 18 32.5 –01 23 10.2–12.5 7 2 Consequently, we had at our disposal photometry of about Ser IV 18 39.0 +00 10 8.0–13.3 45 2 600 stars in total (14 stars are common to the catalogs of SA 110 18 46.5 –01 00 6.9–10.7 30 3 Papers I and II and 8 stars are common to the catalogs of Paper II and SA 110). However, for the investigation of extinc- Publications: (1) Cernisˇ et al. (1997), (2) Straiˇzys et al. (2002c, tion in the area we used 473 stars only, after the exclusion of Paper III), (3) Zdanaviˇcius et al. (1978). binary, multiple and peculiar stars. The map of the investigated area with the sub-areas is shown in Fig. 1. In the present paper we investigate interstellar extinction and cloud distances in a much larger area, covering 5 2. Interstellar extinction law 10 sq. degrees. The area is limited by the following 2000.0 co-× h m h m ordinates: RA from 18 00 to 18 48 and DEC from 3.0◦ We have identified 43 stars from our list with the 2MASS sur- − to +2.0◦. Photometry in the Vilnius system was obtained vey photometry available through the Internet (Skrutskie et al. in 1994, 1997 and 2001 with the 1 m telescope at the 1997). For 19 stars, covering the range of extinctions AV Maidanak Observatory in Uzbekistan. The results of photom- from 0.4 to 2.5 mag, we have calculated color indices V K − etry of 419 stars down to 11 mag and their photometric clas- taking V from Table 1 of Paper II, and color excesses EV K tak- − sification were published by Straiˇzys et al. (2002b), hereafter ing the intrinsic (V K)0 from Straiˇzys (1992, Tables 22–24). Paper II. Spectral types of these− stars were taken from spectroscopic Additionally, 67 fainter stars with V between 10th classification. The least squares solution gives the equation: and 14th mag were observed in four smaller sub-areas situated within the large area indicated above. These sub-areas are listed EV K/EY V = 3.295 + 0.347 (Y V)0 0.464 . (1) − − − ± V. S t r a izys ˇ et al.: Interstellar extinction in the Aquila Rift 587

This equation shows that the ratio EV K /EY V varies from 3.4 for A-type stars to 3.6 for K− giants.− Since the∼ ratio ∼ EY V /EB V 0.8forAstarsand 0.85 for K giants, − − ≈ ≈ Eq. (1) leads to EV K/EB V between 2.7 and 3.1 and RBV = − − 1.1 EV K/EB V between 3.0 and 3.4. These values of RBV are very close− to− the ratio given by the normal interstellar extinction law (Straiˇzys 1992). According to Cardelli et al. (1988, 1989), the form of the extinction law in the visible and the infrared ranges, defining the ratio RBV, is well correlated with its form in the ultravi- olet. Thus, we may accept that in the Serpens dark clouds of medium density the extinction law is normal, i.e., typical for the diffuse dust. This is expected, since the area does not contain young hot and luminous stars which may modify grain sizes in Fig. 2. Interstellar extinction AV plotted against distance r in parsecs for the east part of the Serpens Cauda area with RA between 18h19m the interstellar medium. Only in the dense core of the Serpens and 18h48m. The vertical broken line shows the accepted distance of molecular cloud, in the vicinity of some B-type stars embedded the front dust layer at 225 pc. The broken curves show the limiting in the cloud, Chavarria et al. (1988) and de Lara et al. (1991) magnitude effect for A0 V, A5 V and F0 V stars of V = 12 mag. have found a larger than normal RBV ratio. However, in other parts such interaction between the hot stars and interstellar dust star three closest MK stars were selected. Absolute magnitudes is not observed. Thus, in the calculation of the reddening-free were taken from the MK type tabulation of Straiˇzys (1992). Q-parameters we used the ratios of color excesses correspond- The results of photometric quantification of stars and deter- ing to the normal extinction law. mination of their interstellar extinctions and distances are given in Paper III (Straiˇzys et al. 2002c). For the transformation of 3. Quantification of stars and their interstellar color excesses to interstellar extinctions the normal value of the reddening ratio RYV = AV /EY V = 4.16 was used (Straiˇzys et al. 1996). For the stars in the densest− parts of the Serpens molecular cloud At the beginning all known and suspected binary stars among the larger values of RYV were used (see Sect. 2). The distances r the observed stars were identified and excluded from further in- of the stars were calculated by the equation vestigation of interstellar extinction. For this we have identified V A + 5 A visual binaries in the Washington Double Star Catalog (Mason log r = − V − V (4) et al. 2002). A number of stars were suspected as binaries by in- 5 · specting their images in Internet’s virtual telescope SkyView of The expected errors are: 0.03 mag for EY V , 0.1 mag for AV ± − ± NASA based on the Digital Sky Survey scans of the Palomar and 25% for distance. ± atlas plates (http://skyview.gsfc.nasa.gov). About 8% Papers I and III contain 38 stars closer than 250 pc of stars were suspected as binary or multiple stars since their with photometric distances and Hipparcos parallaxes available. images were found to be non-symmetrical. In some cases close Differences of the photometric and trigonometric distances satellite stars were detected: they also might affect photome- of 32 stars fall within the 25% limits, as expected from the ac- ± try of the main component. The real and suspected binaries are curacy of the photometrically determined absolute magnitudes identified in the catalogs of Papers II and III. and the parallax errors. Larger differences for the remaining For the determination of spectral classes and absolute mag- six stars may be explained by the photometric luminosity er- nitudes of stars from color indices we used the interstellar rors caused by undetected duplicity or peculiarity. These stars reddening-free Q-parameters defined by the equation: are not of decisive importance in the future study of interstellar extinction in the area. A similar comparison of photometric Q = (m m ) (E /E )(m m ) , (2) 1234 1 − 2 − 12 34 3 − 4 and trigonometric distances was done earlier in the California nebula region (Straiˇzys et al. 2001a) and in the Aries molecular where cloud region (Straiˇzys et al. 2002a). In all cases the agreement

Ek,` = (mk m`)reddened (mk m`)intrinsic . (3) of distance scales was found to be sufficiently good, with no − − − systematic differences. Two independent methods described in Straiˇzys et al. (2001b) were applied: (1) the σQ method which uses matching 4. Interstellar extinction versus distance of 14 different reddening-free Q parameters of a program star to those of about 8400 stars with known spectral and luminosity The extinctions AV for stars in the investigated area are plotted classes in the MK system, metallicities and peculiarities and (2) vs. distance in Figs. 2 and 3 for two parts of the area. The divi- the Q, Q method which uses interstellar reddening-free Q, Q di- sion line is at RA = 18h19m, which separates the western part agrams calibrated in spectral classes and absolute magnitudes. (from the Galactic equator to b 7◦) with heavier extinction The last method was used only for G5–K–M stars (the Q , and the eastern part (b 7 11 ∼) with smaller extinction. On UPY ∼ − ◦ QXZS and QXZS QXYZ diagrams). For spectral classes earlier both figures the stars from the main area (Paper II) are plot- than G5 only the σQ method was used. For each program ted as dots, the stars from the molecular cloud area (Paper I) – 588 V. Straiˇzys et al.: Interstellar extinction in the Aquila Rift

selection effect is present. The dotted lines show the limiting magnitude effect at V = 12 mag for the stars of spectral classes A0 V, A5 V and F0 V. The stars of these spectral types above the corresponding curves are accessible only if the V magnitude limit is set at V > 12. The limiting magnitude in various directions of the area varies from 10 to 13. Consequently, the distribution of stars in the figures is strongly affected by selection, and the number of heavily reddened stars at distances >400 pc is considerably reduced. Therefore, we are not able to give any maximum or medium extinction values at these distances. Moreover, a number of more distant dust clouds may be present. However, the lowest extinction value in the area can be estimated with sufficiently high accuracy. Fig. 3. Interstellar extinction AV plotted against distance r in parsecs At distances r > 400 pc it is about 0.5 mag. The stars with for the west part of the Serpens Cauda area with RA between 18h00m such low extinction are seen through windows between the dust and 18h19m. The limiting magnitude curves are described in Fig. 2. clouds. The star BD –01 3542 (V = 9.24) deserves a special dis- as circles, the stars from Areas I to IV – as crosses, the stars cussion. According to Hiltner & Iriarte (1955) its spectral type from SA 110 – as triangles. is B8 Ia:. Nassau & Stephenson (1963) in their Catalog of Figure 2 shows that the majority of stars in the graph form a Luminous Stars in the Northern Milky Way list this star as wedge-shaped belt, which starts at the origin of the coordinates. LS IV –01 4 with spectral type OB+R where R means “red- The stars with nearly zero-reddening extend from the Solar dened”. Bidelman (1988) finds in its spectrum a “very weak vicinity up to 300 pc. The upper limit of the wedge grows broad Hα emission”. Our photometric classification gives a ∼ up with the distance and at 160 pc AV reaches 0.8 mag. Only spectral class B2/3 and a luminosity II–III (uncertain). If the ∼ one star, BD–2 4634 (or No. 31 in Paper II) shows an anoma- star were B3 II–III, its A should be 5.0, M 4.0andthe V V ≈− lous value of extinction: at 104 pc AV is 1.04. It is not excluded distance 440 pc. It is unlikely that so heavily reddened star is at that the star may be an unresolved binary. At 160 pc a sudden this small distance and in the area with a relatively rich Milky increase of AV takes place. The majority of stars continue to Way background. If we accept the B8 Ia type, its AV becomes follow the wedge-shaped pattern, however, a smaller number 4.6 mag, M 7.3 mag and the distance 2.4 kpc. This combi- V ≈− of stars exhibit much larger values of AV : up to 1–3 mag and nation of AV and r seems to be more acceptable, since the star even more. This is an indication that somewhere between 200 is only at +1◦ latitude. The star deserves careful spectral and and 400 pc a network of dense dust clouds starts to appear. photometric investigation. However, these clouds do not cover all the area since many stars Another interesting star from our list is BD –02 4676, with at these distances show only moderate extinction, between 0.4 V = 10.25. This is irregular Lb-type variable CZ Ser of spec- and 1.0 mag. tral class M6 III (photometric classification). The same spectral Let us estimate the distance of the nearest dust concentra- class is given by Hanson & Blanco (1975) from low-dispersion tions. The standard deviation of distances is expected to be objective-prism spectra. The General Catalogue of Variable about 0.25r. This means that the apparently closest heavily Stars (Kholopov 1987) and Sloan & Price (1998) list a spectral reddened± stars may appear at a distance of r 0.25r = 160 pc, − class of M6.5 for the star. The star is an infrared source IRAS i.e., r = 160/0.75 = 213 pc. Another estimation of the front 18347-0241 and it has a circumstellar silicate and CO enve- edge distance of the clouds comes from the unreddened or lope (Sloan & Price 1998; Kerschbaum & Olofsson 1999). We slightly reddened stars, exhibiting the largest apparent dis- obtain its reddening EY V 0.84. If all this reddening is of in- tances. For them r + 0.25r = 300 pc, i.e., r = 300/1.25 = − ≈ terstellar origin, its AV = 3.5 mag, and with MV = 0.0maga 240 pc. Thus, the real distance of the front dark cloud, respon- distance of 225 pc follows. However, since part of the redden- sible for the rise of extinction at r > 160 pc, is between 213 ing is circumstellar, its AV and distance are very uncertain (see and 240 pc, i.e. approximately at 225 56 pc. It is interesting also a discussion of Olofsson et al. 2002). that the stars, exhibiting heavy extinction± within this distance range do not show any correlation with the apparent richness of the background stars. 5. Discussion and conclusions In Fig. 3, which shows the stars at greater distances from the Galactic plane, the extinction up to 100 pc is nearly zero. The investigations described in Paper I and the present paper Beyond this distance, the extinction increases gradually up give evidence that the dust clouds of the Aquila Rift begin at to 300–400 pc and the maximum AV values do not exceed 200–250 pc distance. These clouds cover the whole investi- 1.8 mag. This means that the extinction in the area is much gated area including regions with different richness of the back- lower and more uniform in comparison with lower Galactic ground stars, seen on the red Palomar Sky Survey plates. This latitudes. means that the ornament of dark lanes in the area is formed There is no possibility of estimating the largest extinction by more distant dust concentrations. These dark features are value at different distances, since in Figs. 2 and 3 a strong observable in the Rift up to Galactic latitude of 5 . At higher ∼ ◦ V. S t r a izys ˇ et al.: Interstellar extinction in the Aquila Rift 589 latitudes distant stars of the Milky Way probably are attenuated (http://skyview.gsfc.nasa.gov; Schlegel et al. 1998) by the 200–250 pc clouds only. shows that the investigated area up to b =+5◦ emits a strong There is no direct way to determine how deep the sys- and uniform radiation with some intensity peaks. The strongest tem of the Aquila Rift clouds is. As follows from the appar- source of the far IR radiation is the complex W40 near the ent obscuration of the Milky Way and from the low-velocity star 60 Ser, containing a molecular cloud, a H II region and CO distribution, the Aquila Rift extends by about 20◦ both in a number of point IR sources. This complex is considered to Galactic longitude and latitude. At 225 pc distance this corre- be unrelated with the Aquila Rift, being at a distance of 400– sponds to 82 pc. This value may characterize the cloud system 700 pc (Smith et al. 1985; Vallee & MacLeod 1994; Shuping depth if it is more or less spherical. This diameter of the cloud et al. 1999). Its distance is very uncertain, being determined system fits perfectly the equation between the logarithms of the mostly by the kinematical method, combining radial velocities CO line widths and the logarithms of the cloud radii derived from molecular radio lines and the rotation curve of the Galaxy. by Dame et al. (1985, 1986). Consequently, if the front edge Reyle & Robin (2002) using the Point Source Catalogue of the of the cloud system is at 225 pc and the far edge at 310 pc, DENIS infrared survey have identified a young open cluster in the center distance is at about 270 pc. At this distance from the complex. The extinction AV in front of the complex is es- the Sun the maximal distance of the clouds from the Galactic timated by different authors to be from 9 to 17 mag. Since the planeis70pc( 15 ). Galactic latitude of the complex is +3.5 only, this extinction ∼ ◦ ◦ At about 15◦ longitude the northern part of the Milky Way originates not only in the Aquila Rift clouds. (or the Central Bulge) reappears again, however it is mottled Another somewhat fainter far IR source is the core of the by numerous dark lanes which are very similar to the lanes in Serpens molecular cloud investigated in our Paper I. At higher Serpens Cauda. Probably these dust concentrations belong to Galactic latitudes the dust and CO emission drops out and al- the same cloud system but they are nearer to the center or the most vanishes at b 15◦. Optically, both W40 and the Serpens far edge (up to 310 pc from the Sun). molecular cloud are≥ seen projected on a very dark foreground On the other hand, the Ophiuchus-Scorpio complex of created by the dust lanes of the Aquila Rift. dust and molecular clouds between longitudes 350 0◦ extends The main conclusions of the investigation may be summa- − from 7◦ to +22◦ in latitude. At a distance of the front edge rized in the following items: (1) the front edge of the dark − of the clouds of 150 pc (Straiˇzys 1984, after transforming to clouds in the Aquila Rift is situated at the 225 55 pc dis- the Hyades distance modulus of 3.3 mag) the diameter of the tance, (2) the cloud complex is about 80 pc deep,± (3) the max- clouds is 80 pc, and the center of the cloud system is at a dis- imum extinction in V in the cloud system is close to 3.0 mag, ∼ tance of 190 pc. At this heliocentric distance the height above (4) the objects at low Galactic latitudes (like the star BD – the Galactic plane of 22◦ corresponds to 80 pc. Thus, both the 01 3542 and the cloud complex W40) exhibit much larger ex- ∼ Serpens clouds and the Ophiuchus-Scorpio clouds reach about tinction and are situated far behind the Rift, (5) the Aquila Rift the same distance above the plane. This is an argument for a clouds are similar to the Ophiuchus-Scorpio clouds: both com- common origin of both the Aquila Rift and the Ophiuchus- plexes reach more or less the same maximum height above the Scorpio clouds. A connection of both systems of molecular Galactic plane. clouds has been suspected by Lebrun & Huang (1984) and Dame & Thaddeus (1985) on the ground of the surface dis- Acknowledgements. We are grateful to A. G. Davis Philip and the tribution and radial velocities of CO radio emission. They have anonymous referee for important corrections. also related this cloud system to the clouds in Lupus, on the other side of the Galactic center. Dame et al. (1987) note that all these local molecular clouds can be readily distinguished from References 1 the more distant ones by their low velocity (less than 20 km s− ) and a wide extent to the northern latitudes. Bidelman, W. P. 1988, PASP, 100, 1084 According to Dame et al. (1987) the mass of the Aquila Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1988, ApJ, 329, L33 Rift clouds, estimated from the intensities of CO lines, is about Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245 ˇ 1.5 105 M at a distance of 200 pc. However, the center of Cernis, K., Bartaˇsi¯ut˙e, S., Straiˇzys, V., & Janulis, R. 1997, Baltic Astron., 6, 573 the× cloud system is probably at about 270 pc, i.e., 1.35 times Chavarria, K. C., Ocegueda, J., de Lara, E., Finkenzeller, U., & farther. The new distance leads to the increase of the surface Mendoza, E. E. 1987, in Circumstellar Matter, ed. I. Appenzeller, density of gas by a factor of 1.8. Thus the total mass of the & C. Jordan (Dordrecht: Reidel Publishing Company), IAU Aquila Rift clouds may be as large as 2.7 105 M which × Symp., 122, 97 is still lower than the virial mass of the clouds calculated by Chavarria, K. C., de Lara, E., Finkenzeller, U., Mendoza, E. E., & Dame & Thaddeus (1985) from the radial velocity dispersion Ocegueda, J. 1988, A&A, 197, 151 (or CO line widths) and transformed to the new distance and Dame, T. M., & Thaddeus, P. 1985, ApJ, 297, 751 hence larger cloud radius. Dame, T. M., Elmegreen, B. G., Cohen, R. S., & Thaddeus, P. 1986, The above conclusions about the distribution of the ApJ, 305, 892 molecular and dust clouds receive support from the ex- Dame, T. M., Ungerechts, H., Cohen, R. S., et al. 1987, ApJ, 322, 706 isting Milky Way surveys in the far infrared wave- Dame, T. M., Hartmann, D., & Thaddeus, P. 2001, ApJ, 547, 792 lengths. A glance at the 240, 100 and 50 µm dust de Lara, E., & Chavarria, K. C. 1989, Rev. Mex. Astron. Astrofis., 18, emission maps obtained by IRAS and COBE/DIRBE 180 590 V. Straiˇzys et al.: Interstellar extinction in the Aquila Rift de Lara, E., Chavarria, K. C., & Lopez-Molina, G. 1991, A&A, 243, Skrutskie, M. F., Schneider, S. E., Stiening, R., et al. 1997, in The 139 Impact of Large Scale Near-IR Sky Surveys, ed. F. Garzon et al. Dutra, C. M., & Bica, E. 2002, A&A, 383, 631 (Dordrecht: Kluwer Publishing Company), 25 Eiroa, C. 1991, in Low Mass Star Formation in Southern Molecular Sloan, G. C., & Price, S. D. 1998, ApJS, 119, 141 Clouds, ed. B. Reipurth, ESO Scientific Report, 11, 197 Smith, J., Bentley, A., Castelaz, M., et al. 1985, ApJ, 291, 571 FitzGerald, M. P. 1968, AJ, 73, 983 Straiˇzys, V. 1984, Bull. Vilnius Obs., 67, 3 Forbes, D. 1985, AJ, 90, 301 Straiˇzys, V. 1992, Multicolor Stellar Photometry, (Tucson: Pachart Hanson, O. L., & Blanco, V. M. 1975, AJ, 80, 1011 Publishing House) Hiltner, W. A., & Iriarte, B. 1955, ApJ, 122, 185 Straiˇzys, V., Cernis,ˇ K., & Bartaˇsi¯ut˙e, S. 1996, Baltic Astron., 5, 125 Kerschbaum, F., & Olofsson, H. 1999, A&AS, 138, 299 (Paper I) Kholopov, P. N. (ed.) 1987, General Catalogue of Variable Stars, Straiˇzys, V., Cernis,ˇ K., & Bartaˇsi¯ut˙e, S. 2001a, Baltic Astron., 10, 319 vol. III (Moscow: Nauka Publishers) Straiˇzys, V., Cernis,ˇ K., & Bartaˇsi¯ut˙e, S. 2001b, A&A, 374, 288 Lebrun, F., & Huang, Y.-L. 1984, ApJ, 281, 634 Straiˇzys, V., Cernis,ˇ K., Kazlauskas, A., & Laugalys, V. 2002a, Baltic Mason, B. D., Wycoff, G. L., & Hartkopf, W. I. 2002, The Washington Astron., 11, 231 Double Star Catalog Straiˇzys, V., Cernis,ˇ K., & Bartaˇsi¯ut˙e, S. 2002b, Baltic Astron., 11, (http://ad.usno.navy.mil/wds/wdstext.html) 321 (Paper II) Nassau, J. J., & Stephenson, C. B. 1963, Luminous Stars in the Straiˇzys, V., Bartaˇsi¯ut˙e, S., & Cernis,ˇ K. 2002c, Baltic Astron., 11, 417 Northern Milky Way, vol. IV (Hamburg-Bergedorf) (Paper III) Neckel, Th., & Klare, G. 1980, A&AS, 42, 251 Strom, S. E., Grasdalen, G. L., & Strom, K. M. 1974, ApJ, 191, 111 Olofsson, H., Gonzalez Delgado, D., Kerschbaum, F., & Schöier, F. L. Vallee, J. P., & MacLeod, J. M. 1994, AJ, 108, 998 2002, A&A, 391, 1053 Zdanaviˇcius, K., Gurklyt˙e, A., S¯udˇzius, J., Jaseviˇcius, V., & Reyle, C., & Robin, A. C. 2002, A&A, 384, 403 Kazlauskas, A. 1978, Bull. Vilnius Obs., 49, 3 Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500, 525 Zhang, C. Y., Laurejs, R. J., Clark, F. O., & Wesselius, P. R. 1988, Shuping, R. Y., Snow, T. P., Crutcher, R., & Lutz, B. L. 1999, ApJ, A&A, 199, 170 520, 149